1. Field of the Invention
The present invention generally relates to a toner supplying device for supplying toners contained in a toner container to a developing device and an image forming apparatus using the toner supplying device.
2. Description of the Related Art
Conventionally, in an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, and a multifunctional peripheral combining the above functions, a toner supplying device has been known in which toners contained in a toner container are supplied to a developing device at a position separated from the toner container (for example, in Patent Document 1).
In Patent Document 1, a toner container (toner bottle) which contains toners is detachably disposed from an image forming apparatus main body, and a developing device (process cartridge) is at a position separated from the toner container. In addition, a toner supplying device (toner carrying device) is between the toner container and the developing device. The toner supplying device provides a toner tank (sub hopper) which stores toners supplied from the toner container, a toner supplying pipe which supplies the toners contained in the toner tank to the developing device, and so on. The toner supplying pipe carries the toners in an obliquely downward direction and supplies the toners to the developing device. In addition, a carrying coil is inside the toner supplying pipe. That is, the toner supplying pipe carries the toners in the obliquely downward direction by using a toner carrying force of the carrying coil and the toner's own weight. In other words, the toners slide through the toner supplying pipe.
The toner supplying device suitably supplies the toners to the developing device corresponding to an amount of toners consumed in a developing process in the developing device.
In the image forming apparatus, it is not necessary for the toner container to be adjacent to the developing device. Therefore, the device design freedom is high and the image forming apparatus can be small sized.    [Patent Document 1] Japanese Unexamined Patent Publication No. 2004-139031
However, in Patent document 1, in some cases, the amount of toners to be supplied to the developing device is varied.
Since the toners are carried in the obliquely downward direction in the toner supplying pipe, when the supply of the toners to the developing device is stopped, even if the carrying coil is stopped, the toners remaining in the toner supplying pipe drop into the developing device due to the toner's own weight. That is, in many cases, an amount of the toners more than a target amount is supplied to the developing device. In this case, the concentration of the toners in the developer (the ratio of the toners to the developer) becomes greater than a target concentration, the image density of an output image may become high, toners may be scattered, and the background image may be degraded, due to lowering a toner charging amount.
Even if the toner supplying pipe (toner supplying section) is disposed in the horizontal direction, the above problem occurs. That is, when the toners are supplied to the developing device from the opening of the toner supplying pipe by using the toner's own weight after carrying the toners in the horizontal direction, remaining toners near the opening may be dropped by the toner's own weight right after stopping the carrying coil. In particular, when the liquidity of the toners is high, this problem remarkably occurs.
In order to solve the above problem, by assuming that an excessive amount of toners is supplied to the developing device after stopping the carrying coil, it can be considered that the toner carrying force of the carrying coil is determined to be lower than a predetermined value beforehand. However, in this case, while the carrying coil is driven, the amount of toners to be supplied to the developing device may be insufficient, the image density of the output image may be lowered, and a toner particle in the developer may be adhered onto an image carrier or the output image.
In order to solve the above problem, it can be considered to provide a control unit which controls the amount of toners to be dropped into a toner dropping route from the toner supplying pipe without lowering the carrying force of the toners by the carrying coil. However, when the toners clog at an upstream side of the toner supplying pipe, the amount of toners to be supplied to the developing device by the toner supplying pipe may be insufficient. Consequently, the image density of the output image may be lowered, and a toner particle in the developer may be adhered onto an image carrier or the output image.